The mechanism of active Na ion - transport is considered to require a highly specific ionophoric structure which mediates the flow of energy from ATP to the cation. This energy is released from splitting ATP by (Na plus K ions-ATPase and captured by the "NA ions-carrier" system. Since the cation dependence of the ATPase and of the transport are similar, the Na ion-ionophore may be an intrinsic part of the enzyme. Accordingly, we extracted from known Na ion-transporting system, eel electroplax and beef kidney membranes a peptidic ionophore which increases the conductance of a black lipid membrane. The active material is in the acid soluble fraction of tryptic digest of electrophorous electric organ and beef kidney membrane fractions. The conductance chance elicited by this material is highly selective for Na ion among the other monovalent cations. The increase in conductance of a bilayer membrane is as high as 300 fold after the passage of the material through a DEAE-column. However, the ionophoric activity is lost after treatment with a cation exchange column or after pronase digestion. Gel filtration experiments on P-25 Sephadex indicate that the active material has a molecular weight less than 10,000. Since conductivity increases exponentially with dose of ionophore, the conductive unit may be an oligomer. Thus, the purpose of this project is: to determine the ionophoric ability of the Na ion-specific ionophoric material by two other methods in addition to bilayer assay. Those methods are the organic solvent extraction and the Na ion-specific microelectrode; isolation and purification of a single peptide fragment either from Na plus K ions-ATPase or membrane fraction which has the Na ion-specific ionophoric property; to determine whether the high energy phosphate in the Na ion induced phosphorylated intermediate is attached to the Na ion-specific ionophore; to determine whether the Na ion-specific ionophore acts as a "channel former" or a "carrier"; to determine the ionic interaction between "Na ion-ionophore", K, Mg and Ca and to reconstruct an active transport system from known molecular entities such as "Na ion-ionophore", (Na plus K ions-ATPase, ATP, etc.).